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Roundworms In Dogs: Causes, Risks and Prevention

Imagine this scenario: you’ve just adopted a puppy and he has just vomited up something that looks like a piece of cooked spaghetti.  What’s going on?

Your puppy has probably just demonstrated that he is infected with roundworms.

Roundworms are a helminth parasite.  There are two species that can infect dogs, Toxocara canis and Toxocara leonina. T.leonina can also infect cats. T.canis can also infect humans, with serious consequences.

Puppies frequently are infected with roundworms from their mother.  A pregnant female can pass the parasite to her pups before they are born, or she can transmit them through her milk after delivery.  Roundworms are extremely common in puppies, regardless of where they came from, so all puppies should be given a thorough deworming protocol.

This parasite can also be transmitted by swallowing roundworm eggs from the environment (through normal grooming) or by eating small rodents such as mice that are already infected.

Once the egg is swallowed, they hatch in the intestinal tract and develop into larvae.  The larvae then migrate to other organs, most notably the liver and the lungs.  Larvae in the lungs are coughed up and swallowed, ending up back in the intestinal tract, where they grow into adult worms and lay their own eggs.  Some larvae will stay in the liver, where they encyst.  In this form, the larvae can stay for years, waiting for the right moment.  When that moment comes, the larvae leave the cysts and travel to the lungs.  When an infected dog has a bowel movement, the eggs pass into the environment, where they can infect other dogs, rodents or potentially humans.  It is important to note that fresh feces is not infectious.  The eggs take approximately one month to mature once in the environment, at which point they can be picked up on paws and then swallowed from normal grooming behavior, eaten with grass, etc.  Toxocara canis eggs are well known for their hardiness.  If conditions are not optimal, eggs can remain infective for months or even years.

Symptoms of roundworms are:

  • a pot belly appearance
  • weakness
  • diarrhea
  • vomiting, with or without presence of adult worms
  • poor coat condition
  • belly pain
  • weight loss
  • appearance of adult roundworms in stool

Since roundworms take nutrition from their host, puppies infected with roundworms can suffer from lack of growth, weight loss, and other failure to thrive conditions.  Heavy infections can cause pneumonia or severe diarrhea and vomiting.

Roundworm eggs can be detected with a fecal flotation test, which should be performed yearly.  It is also important to note that a dog or puppy can be infected with roundworms but not actively shedding eggs.  A pup with some or all of the symptoms listed above should still be treated with a deworming medication even if he has a negative fecal flotation test.

Deworming will also only remove the intestinal forms of the parasite and does not address the migrating larval forms.  Once those forms complete their migration and return to the intestine, the dog can still be infected and pass the eggs along to others.  Therefore, repeated deworming is important for breeding dogs, nursing mothers and all puppies.

If your dog has been treated for roundworms, there are several things you can do to minimize reinfection.

  • Pick up all stool immediately and dispose of it.
  • Don’t let your dog use sandboxes or playground areas to defecate.
  • Wash or replace all his bedding and disinfect or replace all his toys and food bowls.
  • Give a heartworm medication that also controls roundworms, such as Sentinel.
  • If you are using an injectable heartworm prevention, talk to your vet about prophylactic deworming on a yearly or twice yearly basis.

Finally, although it is rare, T. canis can infect humans and cause serious eye, heart, lung and neurologic issues.  Kids have a higher risk of becoming infected because transmission is via hand to mouth contact.  Don’t let kids play where dogs defecate and make sure to always wash hands before eating or after handling dog feces.


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